EXPLORING THE DEUTERIUM EXCESS OF ARCTIC PALEOPRECIPITATION USING STABLE ISOTOPE COMPOSITION OF PEDOGENIC PHYLLOSILICATES FROM THE PRINCE CREEK FORMATION (MAASTRICHTIAN) IN NORTHERN ALASKA

Pedogenic phyllosilicates collected from paleosols in the Prince Creek Formation (Maastrichtian) in northern Alaska were analyzed in an effort to reconstruct the isotopic composition of arctic paleoprecipitation. Previous analyses combining oxygen and hydrogen isotope data from multiple sources including pedogenic siderites, dinosaurian tooth enamel phosphates, pedogenic minerals, and n-alkane biomarkers indicated a deuterium excess in arctic paleoprecipitation from the Late Cretaceous. This new dataset provides the first proxy where both hydrogen and oxygen stable isotopic signatures are produced from the same source, thus removing uncertainty from differing biological or chemical processes. The isotopic composition of the pedogenic phyllosilicates for δD range from -93‰ to -72‰ VSMOW and δ¹⁸O ranges from 10.3-11.8‰ VSMOW. The isotopic composition of Late Cretaceous paleoprecipitation was then calculated using the measured isotopic values and combining them with uniquely derived fractionation equations for each phyllosilicate sample and an assumed MAT of 6.3℃. The average δD values of -96‰ VSMOW correspond to δ¹⁸O values of -17.8‰ VSMOW. The calculated results of water isotope δD and δ¹⁸O values from the Prince Creek Formation do not intersect the Global Meteoric Water line, with a deuterium excess ranging from 22-43 per mil. This new dataset not only confirms a deuterium excess in Late Cretaceous high latitude paleoprecipitation, but also provides insight to assessing possible explanations for this phenomenon.